(function() {
  var canvas = document.getElementsByTagName('canvas')[0];
  canvas.width = 800;
  canvas.height = 600;
  var gkhead = new Image;
  var ball = new Image;

  function trackTransforms(ctx) {
    var svg = document.createElementNS("http://www.w3.org/2000/svg", 'svg');
    var xform = svg.createSVGMatrix();
    ctx.getTransform = function() {
      return xform;
    };

    var savedTransforms = [];
    var save = ctx.save;
    ctx.save = function() {
      savedTransforms.push(xform.translate(0, 0));
      return save.call(ctx);
    };
    var restore = ctx.restore;
    ctx.restore = function() {
      xform = savedTransforms.pop();
      return restore.call(ctx);
    };

    var scale = ctx.scale;
    ctx.scale = function(sx, sy) {
      xform = xform.scaleNonUniform(sx, sy);
      return scale.call(ctx, sx, sy);
    };
    var rotate = ctx.rotate;
    ctx.rotate = function(radians) {
      xform = xform.rotate(radians * 180 / Math.PI);
      return rotate.call(ctx, radians);
    };
    var translate = ctx.translate;
    ctx.translate = function(dx, dy) {
      xform = xform.translate(dx, dy);
      return translate.call(ctx, dx, dy);
    };
    var transform = ctx.transform;
    ctx.transform = function(a, b, c, d, e, f) {
      var m2 = svg.createSVGMatrix();
      m2.a = a;
      m2.b = b;
      m2.c = c;
      m2.d = d;
      m2.e = e;
      m2.f = f;
      xform = xform.multiply(m2);
      return transform.call(ctx, a, b, c, d, e, f);
    };
    var setTransform = ctx.setTransform;
    ctx.setTransform = function(a, b, c, d, e, f) {
      xform.a = a;
      xform.b = b;
      xform.c = c;
      xform.d = d;
      xform.e = e;
      xform.f = f;
      return setTransform.call(ctx, a, b, c, d, e, f);
    };
    var pt = svg.createSVGPoint();
    ctx.transformedPoint = function(x, y) {
      pt.x = x;
      pt.y = y;
      return pt.matrixTransform(xform.inverse());
    }
  }

  /**
   * redraw - 重绘
   *
   * @param  {type} ctx description
   * @returns {type}     description
   */
  function redraw(ctx) {
    // Clear the entire canvas
    var p1 = ctx.transformedPoint(0, 0);
    var p2 = ctx.transformedPoint(canvas.width, canvas.height);
    ctx.clearRect(p1.x, p1.y, p2.x - p1.x, p2.y - p1.y);

    ctx.drawImage(gkhead, 200, 50);

    ctx.beginPath();
    ctx.lineWidth = 6;
    ctx.moveTo(399, 250);
    ctx.lineTo(474, 256);
    ctx.stroke();

    ctx.save();
    ctx.translate(4, 2);
    ctx.beginPath();
    ctx.lineWidth = 1;
    ctx.moveTo(436, 253);
    ctx.lineTo(437.5, 233);
    ctx.stroke();

    ctx.save();
    ctx.translate(438.5, 223);
    ctx.strokeStyle = '#06c';
    ctx.beginPath();
    ctx.lineWidth = 0.05;
    for (var i = 0; i < 60; ++i) {
      ctx.rotate(6 * i * Math.PI / 180);
      ctx.moveTo(9, 0);
      ctx.lineTo(10, 0);
      ctx.rotate(-6 * i * Math.PI / 180);
    }
    ctx.stroke();
    ctx.restore();

    ctx.beginPath();
    ctx.lineWidth = 0.2;
    ctx.arc(438.5, 223, 10, 0, Math.PI * 2);
    ctx.stroke();
    ctx.restore();

    ctx.drawImage(ball, 379, 233, 40, 40);
    ctx.drawImage(ball, 454, 239, 40, 40);
    ctx.drawImage(ball, 310, 295, 20, 20);
    ctx.drawImage(ball, 314.5, 296.5, 5, 5);
    ctx.drawImage(ball, 319, 297.2, 5, 5);
  }

  window.onload = function() {
    var ctx = canvas.getContext('2d');
    trackTransforms(ctx);
    redraw(ctx);

    // 鼠标拖动与鼠标缩放
    var lastX = canvas.width / 2,
      lastY = canvas.height / 2;
    var dragStart, dragged;
    canvas.addEventListener('mousedown', function(evt) {
      document.body.style.mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
      lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
      lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
      dragStart = ctx.transformedPoint(lastX, lastY);
      dragged = false;
    }, false);
    canvas.addEventListener('mousemove', function(evt) {
      lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
      lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
      dragged = true;
      if (dragStart) {
        var pt = ctx.transformedPoint(lastX, lastY);
        ctx.translate(pt.x - dragStart.x, pt.y - dragStart.y);
        redraw(ctx);
      }
    }, false);
    canvas.addEventListener('mouseup', function(evt) {
      dragStart = null;
      if (!dragged) zoom(evt.shiftKey ? -1 : 1);
    }, false);

    // 滚轮缩放控制
    var scaleFactor = 1.1;
    var zoom = function(clicks) {
      var pt = ctx.transformedPoint(lastX, lastY);
      ctx.translate(pt.x, pt.y);
      var factor = Math.pow(scaleFactor, clicks);
      ctx.scale(factor, factor);
      ctx.translate(-pt.x, -pt.y);
      redraw(ctx);
    }

    var handleScroll = function(evt) {
      var delta = evt.wheelDelta ? evt.wheelDelta / 40 : evt.detail ? -evt.detail : 0;
      if (delta) zoom(delta);
      return evt.preventDefault() && false;
    };
    canvas.addEventListener('DOMMouseScroll', handleScroll, false);
    canvas.addEventListener('mousewheel', handleScroll, false);
  };
  gkhead.src = 'http://phrogz.net/tmp/gkhead.jpg';
  ball.src = 'http://phrogz.net/tmp/alphaball.png';
})();
